1. Field of the Invention
The present invention relates to a method for the production of 3-bromo-1,1,1-trifluoropropane, and particularly to a method characterized by high conversion, yield and selectivity and using 3,3,3-trifluoropropene as a starting material.
2. Description of the Prior Art
Numerous methods are disclosed in the prior art for the preparation of halogenated alkanes. These methods vary widely, due in part to the different halogens and alkanes involved. The prior art demonstrates that given methods do not readily translate into predictable applications for other compounds. The present invention provides a novel method for the preparation of 3-bromo-1,1,1-trifluoropropane by the addition of anhydrous hydrogen bromide to 3,3,3-trifluoropropene in the presence of an activated carbon catalyst. The reaction is characterized by high selectivity, conversion and yield, and offers significant economic advantages over prior art preparations.
3-Bromo-1,1,1-trifluoropropane is a known chemical, and has found use as a valuable intermediate in the preparation of a variety of useful compounds. For example, 3-bromo-1,1,1-trifluoropropane has been employed in the synthesis of anti-cancer drugs (Japan Kokai Tokyo Koho JP 63156742 and 63156797, 1988; Chemical Abstracts v. 110, 23632 m and v. 109, 190759u), and has also been employed in the synthesis of industrially important phenylalkoxysilanes (e.g., Speierr, et. al, Organometallics, 10(9), 3046 (1991).
3-Bromo-1,1,1-trifluoropropane has been prepared in one prior art process via the treatment of 3,3,3-trifluoropropyl methyl ether (CF.sub.3 CH.sub.2 CH.sub.2 OCH.sub.3) with HBr (Horn, et. al., Chem-Ztg, 105(4), 123, 1981). The starting ether is expensive to produce and, furthermore, the selectivity of the reaction is poor, CF.sub.3 CH.sub.2 CH.sub.2 OH and (CF.sub.3 CH.sub.2 CH.sub.2 O).sub.2 CH.sub.2 also being produced.
U.S. Pat. No. 2,787,646 discloses the preparation of 3-bromo-1,1,1-trifluoropropane in low yield via the reaction of 1-bromo-3,3,3-trichloro-propane and antimony V halides. A similar procedure employing 1-bromo-3,3,3-trichloropropane and antimony trifluoride, SbF.sub.3, also produced 1-bromo-3,3,3-trifluoro-propane in low yield, as described by Chen, et. al., J. Amer. Chem. Soc., 96, 2201 (1974). Treatment of 1,3-dibromo-1,1-difluoropropane (BrCF.sub.2 CH.sub.2 CH.sub.2 Br) with HF in the presence of antimony pentachloride also produced 3-bromo-1,1,1-trifluoropropane in 56% yield.
U.S. Pat. No. 2,644,845 describes the reaction of 1,1,1-trifluoro-propane with bromine to produce 3-bromo-1,1,1-trifluoropropane in 34% yield, along with 2-bromo-1,1,1-trifluoropropane (CF.sub.3 CHBrCH.sub.3) and 3,3-dibromo-1,1,1-trifluoropropane in yields of 17.6 and 19.0%, respectively.
Reaction of 3-iodo-1,1,1-trifluoropropane (CF.sub.3 CH.sub.2 CH.sub.2 I) with bromine has been reported to produce 3-bromo-1,1,1-trifluoropropane, 3,3-dibrom-1,1,1-trifluoropropane and 3-bromo-1,1,1-trifluoro-3-iodopropane in yields of 13%, 26%, and 14%, respectively (J. Chem. Soc., 1951, 2495). Treatment of 3-iodo-1,1,1-trifluoropropane with bromine under ultraviolet irradiation also is known to produce 3-bromo-1,1,1-trifluoropropane (J. Chem. Soc., 1953, 1199).
Henne, et. al., J. Amer. Chem. Soc., 72, 3369 (1950), teaches that due to the powerful electronegative effect of the CF.sub.3 group, the addition of hydrogen halides to 3,3,3-trifluoropropene is difficult. Hence, this addition has been accomplished in the past only via the use of ultraviolet light or powerful Lewis acid catalysts such as aluminum tri-bromide. For example, Henne, op. cit., describes the reaction of 3,3,3-trifluoropropene and HBr at 100.degree. C. in the presence of AlBr.sub.3 to produce 3-bromo-1,1,1-trifluoropropane in 35% yield; the formation of resins in the reaction was also noted. Irradiation of a mixture of 3,3,3-trifluoropropene and hydrogen bromide with a mercury flood lamp for 24 hours in a quartz tube also has been reported to produce 3-bromo-1,1,1-trifluoropropane, for example see Henne, et. al., J. Amer. Chem. Soc., 73, 5527 (1951).
Although the above described methods produce 3-bromo-1,1,1-trifluoropropane, these prior art methods are characterized by numerous disadvantages, including expensive raw materials, poor yields and poor selectivity which preclude their use on a commercial scale.